The present invention relates to integrated circuit test equipment. More particularly, the present invention relates to a method and apparatus for obtaining a timing signal in order to trigger integrated circuit test equipment.
An integrated circuit device typically consists of potentially millions of transistors on a single silicon substrate. Troubleshooting or otherwise probing an integrated circuit device is difficult and time consuming. First, the small size of the microelectronic circuitry combined with the high transistor density makes it difficult to locate faults. Second, because a particular sub-circuit, commonly referred to as a iblock,i on the integrated circuit might operate asynchronously, determining when to examine a particular transistor in the block is problematic. That is, it is difficult to determine when a particular transistor in the block will be switching. This is the result of asynchronous operation which means that the transistors switch independently of any common clock signal that might otherwise act as a block trigger. Third, the fault might not be a manufacturing fault. Rather, it could be a functional fault, meaning that the transistor is functioning as designed, but the sub-circuit design is faulty. In such a case, troubleshooting becomes more complicated because the entire sub-circuit must be evaluated, not just one transistor.
One known manner of troubleshooting or probing an integrated circuit involves physical contact. That is, one must physically connect probes to particular portions of the integrated circuit. The probes can be connected to an oscilloscope or other potential measuring devices. In this way, the potential at a particular transistor can be measured over time.
Contact methods and apparatus like probes have disadvantages. It is difficult to position the probe given the minute size of the microelectronic circuitry under scrutiny. Additionally, the point to be probed may not be readily accessible. For example, the probe point may be difficult to reach given the minute size and multiple layering of the individual integrated circuit elements. For example, the probe point might be beneath the surface of the integrated circuit. In such a case, a probe point hole must be made. If the probe point hole is improperly made, it may result in incorrect measurements. Additionally, the probe hole might damage other lines or channels, resulting in altered circuit performance further frustrating troubleshooting efforts. Where the integrated circuit has test nodes, probing the nodes generally will not yield information as to how specific transistors are operating at a specific time. Other disadvantages of probes include capacitive loading of the circuit caused the probe and associated instrumentation. Capacitive loading can alter the potential of the point being measured. Furthermore, if the point being checked is near a power source or powered line, the probe data might include cross-talk noise.
Non-contact prior art methods and apparatus also have disadvantages. That is, there is no way to utilize non-contact methods on an asynchronous circuit. For example, one non-contact method includes measuring the potential using an electron beam probe. The electron beam probe directs a beam of electrons at a particular conductor in the integrated circuit. By measuring the energy distribution of the secondary electrons produced in response to the electron beam bombardment, the potential at the conductor can be measured.
The disadvantage of the prior art electron beam probe is that it must be turned on and off (triggered) at a particular point in time. This is not difficult for synchronized circuits in which a clock pulse or other synchronized signal can be obtained through contact methods and apparatus. This signal can then be used to trigger the electron beam probe at the appropriate time. But obtaining the synchronization signal through contact methods and apparatus involves the same disadvantages associated with probes discussed above. Moreover, where the sub-circuit under probe is asynchronous in operation, there is no signal available for triggering on the e-beam testor. Therefore, non-contact methods frequently cannot be used on asynchronous circuits.
It can be seen that a non-contact method and apparatus of obtaining a signal to trigger integrated circuit test equipment is needed.